What should I input for "Vehicle Number" if I do not have the transport details before/at arrival?

Travelling to Singapore by Bus
You may wish to submit your declaration on the same day of your arrival when you have the vehicle number. Alternatively, you may submit the declaration beforehand and indicate 'BUS' under Vehicle Number.
When the vehicle number is available, you may update your declaration via:
a) the SG Arrival Card e-Service under "Update a Submission"; or
b) MyICA Mobile App: Select the submitted SG Arrival Card record and tap on the "Edit" button
Travelling to Singapore by Rail
If you are travelling by rail, you may wish to submit your declaration on the same day of your arrival when you have the vehicle number. Alternatively, you may submit the declaration beforehand and indicate 'TRAIN' under Vehicle Number.
When the train number is available, you may update your declaration via:
a) the SG Arrival Card e-Service under "Update a Submission"; or
b) ICA Mobile App: Select the submitted SG Arrival Card record and tap on the "Edit" button.
Travelling to Singapore by Foot
If you are travelling by foot, you may select mode of travel as 'BUS' and indicate 'NA' under Vehicle Number.